The present disclosure herein relates to a semiconductor device, and more particularly, to a semiconductor memory device.
Semiconductor memory devices are essential components in modern digital logic systems such as computers, consumer electronics, and communication devices. Many applications are enabled by a microprocessor or digital controller communicating data with one or more semiconductor memory devices. As digital logic systems are provided to the consumer with ever increasing functionally, reduced power consumption and shrinking physical size, it is necessary to constantly improve the design and manufacturing techniques that yield semiconductor memory devices. Generally speaking, smaller and more densely integrated semiconductor memory devices are demanded that operate at higher speed with lower power consumption.
Semiconductor memory devices may be divided into volatile and nonvolatile semiconductor memory devices. In volatile semiconductor memory devices, data (i.e., logic information) may be stored by setting up or establishing a particular logic state among a set of possible logic states. For example, in a static random access memory (SRAM), a logic state may be set up using a bistable flip-flop element. In a dynamic random access memory (DRAM), a defined quantity of electrical charge is placed on a capacitor element. So long as power is applied to volatile memory devices, stored data may be accessed. Yet, volatile memory devices lose stored data in the absence of applied power.
Nonvolatile semiconductor memory devices include such conventionally understood devise as the MROM, PROM, EPROM, EEPROM, for example. In contrast to volatile memory devices, nonvolatile memory devices are able to retain stored data in absence of applied power. The data state of a nonvolatile semiconductor memory device may be permanent or reprogrammable according to its design and manufacturing techniques. Nonvolatile semiconductor memory devices are used to store program code and/or user (or payload) data across a wide range of applications. Specific memory structures including some additional logic circuits have been developed to optimize the performance for certain application-oriented memory devices.
Some nonvolatile semiconductor memory devices, such as the MROM, PROM and EPROM cannot easily perform erase or write operations. That is, data stored in these specific memory devices may not be readily changed within an incorporating system in response to general application/user requirements. Rather, a cumbersome and externally applied programming apparatus is typically required to alter the data in these memory devices. In contrast, erase and program operations may be electrically performed in the EEPROM. Accordingly, the EEPROM has been widely adopted for use in system programming applications requiring continuous data update or auxiliary memory systems.